Typically, as power systems for an aircraft, three kinds of systems, which are a hydraulic system, a breed air system, and an electric system, are incorporated into the aircraft. The hydraulic system is employed for the operation of landing gears, control surfaces, etc. The breed air system is employed for the operation of air conditioning devices, pressure application devices, de-icing devices, and others, in the interior of the aircraft. The electric system is employed for the operation of electronic devices. In recent years, there has been a trend that at least a portion of the hydraulic system and a portion of the breed air system are replaced by the electric system having a higher efficiency. The aircraft in which the hydraulic system, the breed air system, and other system are replaced as much as possible by the electric system, is typically named MEA (more electric aircraft).
For example, it is known that the breed air system generates a great energy loss. By constructing the breed air system as the electric system, a fuel efficiency can be improved. In the hydraulic system and the breed air system, pipes are required to circulate or send power media (hydraulic oil in the case of the hydraulic system, air in the case of the breed air system), in both of the hydraulic system and the breed air system. For this reason, if at least one of the hydraulic system and the breed air system is constructed as the electric system, piping layout or a mounting work of the pipes can be simplified or omitted, which can reduce manufacturing cost. Moreover, if all of the power systems can be replaced by the electric systems, maintenance of only the electric systems is performed, which allows the power systems to be managed more easily and maintained more easily.
However, with a progress of the MEA in the aircraft, power loads (devices supplied with electric power from the electric systems) supplied with electric power from the electric systems significantly increase in quantity and number. Accordingly, it becomes necessary to increase a power generation capacity. If the power generation capacity is increased, the size of generators increases and wire quantities increase. This would result in an increase in the weight of the aircraft. In view of this, in the progress of the MEA in the aircraft, it is required to avoid and suppress the increase in the weight of the aircraft. For example, Patent Literature 1: Japanese Laid-Open Patent Application Publication No. 2007-015423 discloses that a lightweight and high-efficiency power supply system is provided in all electric aircraft (AEA) by changing a general concentrated power distribution method to a dispersed power distribution method, in an electric system.
FIG. 16 shows an example of an electric system of an MEA at the present moment. In this electric system, two starter/generators are provided for each of a left engine 11L, a right engine 11R, and an auxiliary power unit (APU) 12 in the aircraft. These starter/generators are able to generate AC power of 230 VAC. The AC power of 230 VAC is rectified by automatic transformer-rectifiers (ATRU) 255L, 255R via primary AC power supply buses 211L, 212L, 211R, 212R, and DC power of +/−270 VDC is supplied to motor controllers 331 of power loads 15 via DC power supply buses 241L, 242L, 241R, 242R. Under control of the motor controllers 331, driving motors (M in FIG. 14) included in the power loads 152 are actuated.
In implementation of the MEA in the aircraft, it is required that an electric system be stabilized by suppressing a change (fluctuation) in a power supply voltage as well as addressing the increase in a power generation amount. For example, if regenerative power occurs in a load in which greater regenerative power (return of electric power) occurs as compared to another load, such as an actuator for controlling a control surface, a voltage in the electric system significantly increases temporarily (for a specified time). Or, if the power loads to be supplied with the electric power increase in number temporarily, a significant voltage decrease (drop) occurs.
Various approaches for avoiding or suppressing the change in the power supply voltage have been proposed so far. For example, to address the above stated problem associated with the regenerative power from the great load, it is known that a resistor is built into a controller of the load (e.g., actuator). In accordance with this configuration, the regenerative power is converted into heat by the resistor and consumed. That is, the regenerative power is prevented from returning to the electric system. To address the voltage decrease (drop) due to the temporary increase in the loads, it is known that AC power generators having a power generation capacity made greater to correspond to the degree of the voltage decrease. Also, Patent Literature 2: US Patent Publication NO. 2009/0302153 discloses an electric system in which surplus electric power such as regenerative power is absorbed or deficient electric power due to a voltage decrease is made up for, by using a DC power supply such as a battery or a capacitor, in a small-sized aircraft.